Method for on demand power production utilizing geologic thermal recovery

ABSTRACT

Methods for providing on demand power to an end user in a variety of embodiments are disclosed. Closed loop thermal recovery arrangements are disposed within a geologic formation having a predetermined potential thermal output capacity. A power generation device is incorporated in the loop to recover energy. A working fluid is circulated within the loop at varying flow rates to oscillate thermal output about the predetermined potential thermal output capacity, to produce on demand power where the average thermal output may equal the predetermined potential thermal output capacity. Integrations with intermittent renewable energy sources are provided which optimize performance and distribution.

FIELD OF THE INVENTION

The present invention relates to closed loop energy recovery from ageologic formation having extractable heat and more particularly to amethod for providing on demand energy using a closed loop productionsystem.

BACKGROUND OF THE INVENTION

The previous activity in the geologic heat/power production art has beenwell documented. One of the early examples is found in United StatesPatent Publication 20120174581, Vaughan et al, published Jul. 12, 2012.

Other examples include United States Patent Publication 20070245729,Mickleson, published Oct. 25, 2005, McHargue, in United States PatentPublication 20110048005, published Mar. 3, 2011, Lakic, in U.S. Pat. No.8,281,591, issued Oct. 9, 2012, and most recently U.S. Pat. No.10,527,026, Muir et al, issued Jan. 7, 2020.

These references are representative of the progenitor developments inthe thermal recovery for power production body of prior art. Althoughuseful as such, they are not instructive or definitive in addressingpower production demand issues and how these are intermingled withintermittent renewable energy sources.

Intermittent renewables have recently become competitively priced withfossil fuels, and now produce a large fraction (30-45%) of electricityin certain jurisdictions (California, Germany, etc).

These carbon-free sources have potential to dramatically reducegreenhouse gas emissions. However, there is a limit to how muchsolar/wind can be brought onto a power grid, driven by the inherentintermittency of the energy generation. These intermittent or variablegeneration sources are also referred to as non-dispatchable.

High penetration of solar/wind in power grids causes issues with systemintegration due to the difficulty of replacing the energy produced whenthe sun is not shining, and the wind is not blowing. This is epitomizedin California which has high solar penetration and creates what iscolloquially known as the “duck curve”;(https://en.wikipedia.org/wiki/Duck_curve).

Currently in California, solar plants cannot be built without somemeasure of energy storage, typically 2-4 hours of lithium-ion batterystorage. However, true energy storage capability of 8 hours or more isprohibitively expensive.

A comprehensive report on electricity sources written by NREL“Electricity Generation Baseline Report”(https://www.nrel.gov/docs/fy17osti/67645.pdf) describes the issues inintegrating non-dispatchable technologies. Currently, there is no viablesolution to decarbonize the remaining approximately 50% of the grid.

Another problem with integrating intermittent renewable energy sourcesis that they tend to decline very rapidly, called downward fast-ramping.Accordingly, an important and valuable feature desired in dispatchablepower sources is an upward “fast-ramping” capability to offset the quickdeclines from wind/solar. Many technologies lack this fast rampingability (for example coal, nuclear, and some types of gas generation arenot fast ramping).

The challenge is to develop a cost-effective energy system to dispatchthe evening and night-time load when solar/wind are unavailable.

Traditional geothermal would seem a natural fit to provide renewabledispatchable power. However, traditional geothermal systems operate in abaseload fashion due to several fundamental issues which prohibit theability to provide flexible/dispatchable power output.

Flow from the geothermal reservoir cannot be accelerated withoutincurring massive parasitic pumping losses. This is due to theDarcy-Flow and fracture-flow regimes within the rock reservoir;significant energy is required to accelerate flow rates above the normalbaseload operating point.

The reservoirs can be pressurized however, this may cause loss ofreservoir containment, induce fracturing and cause induced seismicity.

In addition to the parasitic losses which negate any gross powerincrease while ramping, in traditional geothermal there are numerousoperational issues caused by ramping flow up and down significantly,sand production, liner failure, pump operating ranges, liquid/gas flowregime variability, thermal expansion and cooling processes causinggeomechanical issues within the reservoir, injector well plugging, etc.

In a request for proposal from the United States Department of Energy,(https://www.sbir.gov/sbirsearch/detail/1523867), it was indicated:

“Dispatchable generation refers to sources of electricity that can beturned on or off, or can adjust their power output accordingly to anorder. Geothermal plants are usually used for base-load power ratherthan dispatchable power. The 8 MW Puna Expansion Facility in Hawaii isthe first fully dispatchable geothermal power plant (Nordquist et al.,GRC Transactions, Vol. 37, 2013). As described by the Ormat team, theadaptation of a base load power plant to full dispatchability was noteasy. The plant is required to adjust its power output quickly inresponse to a requested ramp rate and maintain its frequency withinclose tolerance to the grid power. This was a challenge for a geothermalplant because the heat source does not naturally respond quickly tochanges in demand. To address this challenge, Ormat decided to maintainthe geothermal fluid flows at relatively steady rates while providing abypass around the generation equipment as needed. Under part load, someof the geothermal fluid is pumped to the surface, bypasses thegeneration equipment, and is re-injected to the ground withoutextracting any useful enthalpy. This approach is robust but necessarilyincurs high parasitic power draws at part load due to the constant,full-flow pumping power requirements.”

This geothermal reservoir (the subsurface system) in the above exampleis not produced at full capacity. The so-called dispatchability is, inreality, just operating with a low capacity factor, based on thegeothermal subsurface capacity, or operating the system below thepotential thermal output capacity of the geothermal system for most ofthe time and operating equal to the potential thermal output capacitywhen dispatching.

Other researchers have focused on using the subsurface as a storagemedium for air—reservoir Compressed Air Energy Storage; CO2—in thearticlehttps://asmediqitalcollection.asme.org/memaqazineselect/article/137/12/36/380449/Earth-BatteryCarbon-Dioxide-Sequestration-Utility,or pressurized water. These systems all face similar drawbacks. Thecritical issue is they are open systems (the volume of working fluidwithin the system is constantly changing) and so suffer from thechallenges of controlling and managing flow in porous media andextensive, variable fracture networks. Furthermore, they are primarilyenergy storage systems, rather than energy producing systems.

Still other researchers have looked at using Thermal Energy Storage,(TES), systems at surface to store heat produced by geothermal systemsto optimize daily energy output to the end-user. However, a keychallenge is the loss in temperature due to sensible heat exchangers,and the resulting lower round-trip efficiency. Furthermore, theinstalled cost of a large-scale TES for high temperatures suitable forelectricity generation is currently prohibitive.

A much different, but still relevant field of prior art islow-temperature Underground Thermal Energy Storage systems. These comein two varieties, Borehole Thermal Energy Storage (BTES) and AquiferThermal Energy Storage (ATES). ATES and BTES are essentially lowtemperature heat-pump systems that store and drawdown seasonal energy,from summer to winter and vice-versa. BTES stores heat from airconditioning waste heat in the summer, via conductive heat transfer withthe surrounding rock, then drawdown that heat in the winter. Both ATESand BTES are not energy-generating systems, or even simple energystorage systems. Rather they work in conjunction with an energy-drivenheat pump and the full system is an energy consumer, although moreefficient than standard AC and space heating technologies.

Cryogenic air storage is an attractive technology to store excesselectricity generated by renewable systems and discharge when required.The round-trip efficiency of the storage technology increases when usedin conjunction with geothermal heat. This type of integration has beeninvestigated by some researchers, for example cetin et al in “Cryogenicenergy storage powered by geothermal energy”, vol 77 Geothermics, 2018).

The above academic paper considers a geothermal system which is operatedin a baseload fashion, rather than a dispatchable geothermal systemdisclosed herein. The primary challenge of this methodology and otherprior art is that the cryogenic discharging happens over several peakhours, however the geothermal heat output is baseload (i.e. flat outputover 24 hours).

What is required to ameliorate the issues with current technologies andbaseload limitations is a new paradigm that provides on demand power toan end user at any time and supplements and optimizes intermittentrenewables when required.

The present technology to be discussed further herein addresses all ofthe issues currently in power generation, infrastructure anddistribution without reliance on baseload sources, non-dispatchablerenewables, or batteries.

SUMMARY OF THE INVENTION

One object of one embodiment of the present invention is to provide amethod to produce dispatchable, scalable and fast-ramping electricityutilizing a closed-loop engineered geologic thermal recovery system.

A further object of one embodiment of the present invention is toprovide a geothermal power output system having baseload distributionsubstantial equivalent with oscillated discontinuous output cyclesaveraged over a distribution period.

Another object of one embodiment of the present invention is to providea method for optimizing the characteristic potential thermal outputcapacity of a well system including a working fluid capable of thermalcharging from the formation, the system having an inlet well and anoutlet well and disposed within a formation having the characteristicpotential thermal output capacity, comprising: modulating circulation ofthe working fluid within the well system to oscillate thermal outputfrom thermally charged working fluid about the characteristicpredetermined potential thermal output capacity, where the averagedoscillated thermal output substantially equates with the predeterminedpotential thermal output capacity of the formation.

In this embodiment, the thermal output is inconstant and is cycledbetween a charging operation where the working fluid is thermallycharged through conductive heat transfer from the formation and adischarging operation where the thermal energy is removed forprocessing.

Processing may comprise conversion to at least one of electrical energy,heat energy and combinations thereof.

In respect of the modulation, this may take many forms including atleast one of variation in flow rate of the working fluid, residency timein the system, oscillation duration, thermal charging duration, thermaldischarging and combinations thereof.

Practice of the method allows for generating on demand energy to an enduser through interaction between the charged working fluid and a powergeneration device.

A further object of one embodiment of the present invention is toprovide a method for providing on demand power to an end user with awell system having an inlet well, an outlet well in a thermallyproductive geologic formation, comprising: forming a closed loop with apower generation device operatively connecting the inlet and the outlet;circulating a working fluid in the loop with a predetermined residencytime to thermally load circulating working fluid through conduction fromthe formation; and modulating the flow rate of thermally loaded workingfluid within the loop for power generation based on user demand.

Depending on the specific parameters attributed to the formation, theinlet well and the outlet well may be operatively and fluidly connectedwith a interconnecting section being disposed for conduction in thethermally productive geologic formation.

For enhancing thermal recovery and networking of well systems amongst ahost of other advantages, the inlet well and the outlet well may beconnected with a plurality of interconnecting sections in apredetermined pattern within the formation. Owing to Applicant'spatented and published technologies, patterning of the well systems,interconnecting segments, networks of well systems is simplified andunrestricted from a systems design perspective.

For power creation, output management and dispatchability, selectivemodulation of the circulation of the working fluid may be conductedwithin predetermined sections of the plurality of interconnectingsections of the well system to oscillate thermal output from thermallycharged working fluid about a characteristic predetermined potentialthermal output capacity of the formation, where the averaged oscillatedthermal output substantially equates with said predetermined potentialthermal output capacity of said formation.

Where the well system includes a plurality of well systems with aplurality of interconnecting sections, selective modulation of theworking fluid may be effected in the individual interconnecting sectionsof the well systems, in some or all of the interconnection sections atspecific times and in specific sequences as well with adjacent wellsystems in a user selected manner.

The method is predicated on flexibility in deployment and accordingly,any geologic formation having a temperature of greater than 90° C. canbe exploited regardless of the type of rock, i.e. high permeability, lowpermeability, hot dry rock, a geothermal formation, a sedimentaryformation, a volcanic formation, a variable permeability formation andcombinations thereof. In furtherance of the flexibility, the methodologyis not limited by rock formation incongruities, i.e. naturally fissured,fractured or cracked rock, synthetically fissured, fractured or crackedrock and combinations thereof. The method can be applied in anyscenario.

In respect of a working fluid, a desirable fluid may be water which mayinclude a drag reducing additive such as a surfactant, a polymericcompound, a suspension, a biological additive, a stabilizing agent,anti-scaling agents, anti-corrosion agents, friction reducers,anti-freezing chemicals, biocides, hydrocarbons, alcohols, organicfluids and combinations thereof.

Other suitable fluids may comprise super critical carbon dioxide, loweralkanes, e.g. C1-C10, fluids containing phase change materials,refrigerants. The examples are numerous and readily derivable from theprior art.

Additives to promote the maintenance of the well system are contemplatedfor use in the working fluid as are compounds to augment thethermodynamic efficiency of the working fluid.

Yet another object of one embodiment of the present invention is toprovide a method for providing on demand energy to an end user with ageothermal mechanism, the mechanism including an inlet well, an outletwell and an interconnecting section there between in a geologicformation, comprising: forming a closed geothermal loop with a powergeneration device connecting the inlet and the outlet; circulating aworking fluid in the loop with a predetermined residency time tothermally load circulating working fluid through conduction from theformation; and adapting the flow rate of thermally loaded working fluidwithin the loop based on user demand.

The geothermal wells and interconnecting section may be newly formed orexisting. If existing, the methodology herein can be easily adapted toretrofit an existing installation for enhanced efficiency.

The energy may be electrical or heat energy depending on the proposedend use with residency time sufficient to facilitate power generationfor the duration of a user's demand.

Interaction between the charged working fluid and a power generationdevice within the loop includes minimizing residency time by increasingthe flow rate of the charged working fluid.

For further added efficiency, thermal energy from the charged workingfluid may be stored in the geothermal formation and the working fluidmay be supplemented with energy charged working fluid from adjacentwells in the formation. The supplementation may take the form ofrerouting working fluid from adjacent wells to a well and powergeneration device under user demand.

Yet another object of one embodiment of the present invention is toprovide a method for delivering on demand power to an end user,comprising: providing an inlet well, an outlet well and a wellinterconnecting section between the inlet well and the outlet well andbeing disposed within a geologic formation having a temperature of atleast 90° C., the formation having a predetermined potential thermalcapacity; implementing a closed loop arrangement within the formationthrough connecting the outlet well to a power generation device torecover energy from the well arrangement in a closed loop between thewells and the power generation device, the closed loop arrangementhaving a predetermined energy output within available potential thermalcapacity; circulating a working fluid within the loop with predeterminedresidency time at least within the interconnecting section to maximizeenergy transfer from the formation to form an energy charged workingfluid; and generating on demand energy to an end user throughinteraction between the charged working fluid and the power generationdevice.

Consistent with the flexibility already established herein with themethod, the interconnecting section(s) may be cased, uncased, lined,chemically treated for augmented conductivity, chemically sealed,self-healing when sealed, thermally sealed, include single pipeoptionally perforated, coaxial pipe optionally perforated andcombinations thereof in a continuous or discontinuous configuration. Theworking fluid can be designed to maintain wellbore integrity by sealingfractures or generated permeability. If the wellbore is at risk ofbreakouts or compressive failure, the fluid density may be increased toprovide sufficient compressive strength on the formation. Conversely, ifthe formation is cooled sufficiently it may be at risk of tensilefailure, in which case the fluid may be selected to have reduceddensity.

The working fluid may be circulated within the loop at varying flowrates to oscillate thermal output about the predetermined energy outputcapacity, to produce on demand power where the average thermal outputmay equal the predetermined potential thermal output capacity.

In alternative embodiments, a plurality of interconnecting sections(multilaterals) common to the inlet well and the outlet well aredisposed in a configuration to maximize thermal recovery from a heatgradient of said formation. If a footprint for the arrangement is anissue, the inlet and outlet wells may be co-located.

In further alternative embodiments and to exploit the thermal gradientwithin the formation, the interconnecting sections may be arrangedsymmetrically relative to adjacent interconnecting sections,asymmetrically relative to adjacent interconnecting sections ininterdigital relation to adjacent interconnecting sections, in coplanarrelation to adjacent interconnecting sections, in parallel planarrelation to adjacent interconnecting sections, in isolated or groupednetworks and suitable combinations thereof.

For purposes of improved distribution which will be further elucidatedherein after, a plurality of closed loops with outlet wells of adjacentloops may be selectively connected to inlet wells of additional wellstaking the form of a daisy chain configuration which further may bevalved for user selectivity.

Another object of one embodiment of the present invention is to providea method for optimizing power distribution on a pre-existing grid,comprising: providing an intermittent power production arrangementhaving a designed maximum power production quantity and a secondeffective power production quantity on the pre-existing grid;positioning an energy recovering and producing closed loop within athermal bearing geologic formation adjacent the intermittent powerproduction arrangement, the loop including an inlet well, outlet well,interconnecting segment between the inlet well and the outlet well, theinterconnecting segment positioned in the formation to facilitatethermal recovery in the formation, the formation having an availablepotential thermal capacity; positioning the closed loop in aconfiguration within the formation to produce a predetermined energyoutput from the available potential thermal capacity; circulating aworking fluid within the loop with a predetermined residency time tothermally charge circulating working fluid through conduction from theformation; and selectively thermally discharging the working fluidthrough the intermittent power production arrangement to increase powerproduction to a quantity above the second effective power productionquantity and below the designed maximum power production quantity,whereby overall power production is optimized using the pre-existinggrid.

The intermittent power production arrangement and the energy recoveringand producing closed loop may be positioned on a common geographicfootprint to produce on demand energy.

Selective thermal discharging of the working fluid through theintermittent power production arrangement is effected during periods ofsignificant user power demand and transmitted using the transmissioncapacity and infrastructure of the pre-existing grid of the intermittentpower production arrangement. The intermittent sources are widely knownas wind, solar and battery sources.

A still further object of one embodiment of the present invention is toprovide a power production method, comprising: providing a powertransmission grid for transmitting produced power to an end user, thegrid having an output capacity; providing a power production arrangementhaving a designed maximum power production quantity and a secondeffective power production quantity on the grid; positioning an energyrecovering and producing closed loop within a thermal bearing geologicformation adjacent the intermittent power production arrangement, theloop including an inlet well, outlet well, interconnecting segmentbetween the inlet well and the outlet well, the interconnecting segmentpositioned in the formation to facilitate thermal recovery in theformation, the formation having an available potential thermal capacity;positioning the closed loop in a configuration within the formation toproduce a predetermined energy output from the available potentialthermal capacity; circulating a working fluid within the loop with apredetermined residency time to thermally charge circulating workingfluid through conduction from the formation; and selectively thermallydischarging the working fluid through the power production arrangementto maintain power production to the capacity throughout the powertransmission grid.

The power transmission grid may include a plurality of separatedistribution zones for distribution of power over a geographic area withat least some of the zones including an energy recovering and producingclosed loop.

Accordingly, a further object of one embodiment of the present inventionis to provide a power plant for providing user predetermined powerdistribution, comprising: a thermal energy recovery apparatus configuredto modulate the circulation of a working fluid in a thermally productiveformation whereby thermal energy is transferred into the working fluid,the apparatus for oscillating discontinuous output cycles averaged overa distribution period; and distribution apparatus for distributingaveraged power output as a user predetermined power output.

Having thus generally described the invention, reference will now bemade to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an energy recovery arrangementdisposed in a thermal bearing geologic formation;

FIGS. 2A through 2D are schematic illustrations of alternativeinterconnecting sections or multilateral sections for use in therecovery arrangement;

FIG. 3 is an alternative for the recovery arrangement;

FIG. 4 is a graphical representation of a series of operating scenariosdepicting temperature (thermal output) as a function of time for eachscenario;

FIG. 5 is a graph, similar to that in FIG. 4, with the data presentedover several days;

FIG. 6 is a schematic illustration of the thermal output over 30 yearsof specific scenarios referenced in FIGS. 4 and 5;

FIG. 7 is a schematic illustration of a dispatchable geothermal systemintegrated with other non-dispatchable renewables;

FIG. 8 is a schematic illustration of multiple dispatchable geothermalloops in a network;

FIG. 9 is a flow diagram illustrating the process to plan, control, andoptimize the integration of non-dispatchable renewables with adispatchable geothermal system;

FIG. 10 is a schematic illustration of the combined power outputcapacity of a network of power generators;

FIG. 11 is a schematic illustration to mitigate electrical gridsaturation with intermittent sources of power; and

FIG. 12 is a schematic illustration of an alternate embodiment of thepresent invention.

Similar numerals used in the Figures denote similar elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 illustrates an example of theoverall arrangement used to practice embodiments of the methods to bedelineated herein. Numeral 10 globally references the overallarrangement. A geologic formation 12 having thermal energy having atemperature of at least 90° C. and which may be and typically above 150°C., or even 600° C. or greater, includes a subterranean loop arrangementhaving an inlet well 14 and an outlet well 16, which may be co-located,interconnected with at least one interconnecting section 18. In theexample, several sections 18 are depicted. The thermal gradient willdepend on the formation characteristics.

At the surface 20, inlet 14 and outlet 16 are connected to a powergeneration device 22. Device 22 completes the loop arrangement as aclosed loop which will be referenced for simplicity as L. As will beevident, the sections 18 are disposed within the geologic formation forthe purpose of recovering thermal energy from the surrounding formation12. For clarity, the closed loop, L, and particularly, sections 18 mayinclude fissures, fractures, cracks within which fluid may betransported, however, this will not detract from the point of the closedloop concept; despite the fact that there may be localizedmultidirectional flow anomalies, the flow pattern remains closed in theinlet, interconnect, outlet, power generation device 22 combination ofelements.

The geologic formation may be any formation that provides a temperatureas noted above. In this regard, examples include a geothermal formation,a low permeability formation, hot dry rock, a sedimentary formation, avolcanic formation, a high temperature formation, a variablepermeability formation and combinations thereof. These are examplesonly; any number of others are within the purview of the invention.

The formation, depending on its nature will have a predeterminedpotential thermal output capacity which can be analyzed in advance bysuitable techniques known to those skilled in the art. Each formationwill, of course, have a different output capacity.

In consideration of this, each loop, L, will have a predeterminedpotential thermal output capacity which is reflective of its designparameters, such as number of sections 18, geometric arrangementthereof, depth, length, formation temperature, formation rockproperties, inter alia. All of these parameters will be apparent tothose skilled.

For recovery, a working fluid is circulated through the loop, L, andexits the outlet well 16 flows through power generation device 22 whichconverts thermal and/or kinetic energy into electricity for use by anend user globally referenced with numeral 24 and/or is redistributed at26 for alternate uses to be discussed herein after. Once circulated asindicated, the working fluid is reintroduced to the inlet 14.

The working fluid is thermally “charged” or loaded by circulating theworking fluid through the closed-loop, L, at a relatively low flow rateduring the charging period. The residence time of the working fluidwithin the subsurface flow path is increased, and hence the fluid isheated up to a high temperature via conductive heat transfer with thesurrounding formation 12.

The system is “discharged” by increasing the flow rate significantly andflushing out the volume of heated working fluid within the hotsubsurface portion of the closed circuit, L.

The working fluid may comprise water, super critical carbon dioxide,etc., and include a drag reducing additive such as a surfactant, apolymeric compound, a suspension, a biological additive, a stabilizingagent, anti-scaling agents, anti-corrosion agents, friction reducers,anti-freezing chemicals, biocides, hydrocarbons, alcohols, organicfluids and combinations thereof. Other suitable examples will beappreciated by those skilled. It is contemplated that the working fluidmay be compositionally modified dynamically where changing subsurfacethermal characteristics dictate.

Referring now to FIGS. 2A, 2B, 2C and 2D, shown are schematicillustrations of the possible dispositions and combinations of theinterconnecting sections 18. The illustration generally shows that theadjacent interconnecting sections may be symmetrical, asymmetricallyrelative to adjacent interconnecting sections, in interdigital relationto adjacent interconnecting sections, in coplanar relation to adjacentinterconnecting sections, in parallel planar relation to adjacentinterconnecting sections, in isolated or grouped networks andcombinations thereof. Specific geometric disposition will vary on thetemperature gradient characteristics. The Figures are exemplary only;suitable variations will be appreciated by the designer.

FIG. 3 illustrates an example where the loop, L, includes a plurality ofinterconnecting sections 18 with the output 16 of one section 18 servesas the input 14 of an adjacent section 18 with common collection atpower generation device 22. In this manner the loop, L, is subdividedinto a daisy chain configuration for operation of the method.

The potential thermal output capacity is the maximum sustainable thermalenergy output of the system. Thermal output may be varied temporarilywith the methodology disclosed herein, but the long-term average output(i.e. averaged over months or years) cannot exceed the potential thermaloutput capacity.

The overall geothermal efficiency of a system is equal to the averagethermal output divided by the potential thermal output capacity, what istypically referred to as geothermal “capacity factor”. It isadvantageous to have a high capacity factor, or high utilization of theavailable potential thermal output capacity. Conventionally this isachieved by constant thermal output at or near the potential thermaloutput capacity. Many geothermal systems operate at >90% capacity factorin this manner, sometimes referred to as “baseload” operations. Thedisclosed methodology enables a high geothermal capacity factor whilealso providing flexible on-demand energy output rather than a constantoutput.

FIG. 4 illustrates an example based on transient thermodynamic modellingof a closed-loop multilateral system described in Applicant's co-pendingApplication No. PCT/CA2019000076, among others. The inputs for thethermodynamic model are tabulated below.

FIG. 4 Example Data

Vertical In Vertical Out Laterals Total Length 4810 4810 5648 Casing ID(mm) 215.9 215.9 215.9 Casing OD (mm) 244.5 244.5 NA Cement OD (mm)298.5 298.5 NA Rock Thermal Conductivity 3.2 3.2 3.2 (W/m. K) Roughness(mm) 0.05 0.05 0.15 Elevation In 0 −4415 −4415 Elevation Out −4415 0−4415 Number of lateral legs 12 Surface Temperature (° C.) 10Temperature Gradient (° C.) per km 34.3 Bottom Hole Temperature (° C.)161.3 Rock Density (kg/m3) 2663 Rock Specific Heat (J/kgK) 1112

The figure shows three operating scenarios for the same geothermal loop:operating in a baseload manner with a constant flow rate (Base Case), inwhich case the thermal output equals the potential thermal outputcapacity; operating with a charging cycle for 16 hours at 33 kg/s andthen discharging for 8 hours at 130 kg/s; and operating with a chargingcycle for 12 hours at 30 kg/s and then discharging for 12 hours at 100kg/s.

Typically, the charging cycle would be done when the energy price is lowor there is an excess of variable renewable supply. This allows theinterconnecting sections 18, referenced herein previously to recover thethermal energy from the formation.

FIG. 5 illustrates focused details over the timeframe of 3 days. Theaverage flow rate over the combined charge/discharge periods isapproximately equal to the optimum fixed flow rate if the system wasoperated in a baseload manner. In this example, the same subsurface wellarrangement as noted in the earlier Figures, if it were operated in abaseload manner, would equal the potential thermal output capacity atall times when the flow rate is equal to 60 L/s. In the vernacular, thesystem would operate at the full subsurface geothermal capacity. This isa critical differentiator from some prior art (Ormat at Puna) where theaverage geothermal output over combined “charging” and “discharging”cycles is significantly below long-term capacity.

The charging cycle establishes a strong thermosiphon, driven by thedensity difference of the cold fluid in the inlet well 14 compared tothe hot fluid in the outlet well 16. During the charging cycle, thethermosiphon pressure drive is higher than required to maintain thedesired flow rate. Flow rate is therefore controlled by choking flowdownstream of the outlet well 16, using a flow-control valve or otherapparatus (not shown) to apply a pressure-drop. The flow-control valveis automated and may be controlled with software that uses athermodynamic model to calculate the required position of the valve. Thecontrol valve also helps manage the pressure in the subsurface loop, tokeep it within desirable bounds based on the density of the workingfluid and pump discharge pressure.

When discharging, flow rate can be immediately increased by releasingthe choke (opening the control valve). This near-instantaneous increasein flow rate enables a fast-ramping capability. Flow rate can beincreased to until the hydraulic pressure losses through the closedcircuit loop equal the thermosiphon pressure drive.

Flow can be increased beyond this level using a pump, which wouldrequire a parasitic power load. However, as long as the majority of thepressure drive is generated by the thermosiphon effect, the parasiticload is practically acceptable.

Using these methodologies, flow rate can be controlled to match poweroutput to the end-user demand, through both the charging and dischargingcycles and residency time of the working fluid in the loop.

In the prior art traditional open geothermal systems or flow in porousmedia, the pumping pressure required to reach the high flow rates whiledischarging cause an unacceptably high parasitic pump load anddrastically reduce or eliminate any gains in net power output. It hasbeen found that the practical limit is achieved when the ratio of thepressure losses in the circuit to the thermosiphon pressure drive isapproximately 1.5. The system must be designed to have a hydraulicpressure loss less than 1.5 times the thermosiphon pressure drive.Ideally, pressure losses are less than 1 times the thermosiphon driveand the entire flow is driven by the thermosiphon. Accordingly, there isno parasitic pump load.

Energy is stored within the working fluid itself. During the chargingcycle, sufficient residence time is required to heat the working fluidenough to accommodate the discharge cycle. For example, if the dischargecycle is typically 8 hours long, the fluid circuit transit time must beat least 8 hours (averaged over both discharge and charge cycles).

During the charging cycle, energy can also be stored temporarily in rockadjacent to the subsurface flow path and outlet well 16. At low flowrates, heat is transferred conductively from hotter rock in theformation 12 into the working fluid and as the fluid progresses throughthe system, it encounters cooler rock (typically shallower, for examplein the outlet well 16), where energy is transferred from the fluid tothe cooler rock and stored temporarily. During the discharging cycle,the average fluid temperature drops, and the stored heat is transferredback into the working fluid.

A closed loop avoids the operational problems with traditionalgeothermal systems, which are exacerbated when varying the flowdrastically as discussed herein. For example, common operational issuesare caused by brine, solids, scaling, plugging, and dissolved gases.

The dispatchability disclosed herein integrates well with cryogenic airstorage (CES), hydrogen production, or other systems that use storedelectrical energy. An example of the process flow is shown below. TheCES charging cycle can use cheap excess power from the grid orco-located renewables (for example, solar during the peak daytimehours). The CES can also use produced geothermal power to charge but isnot necessary. In one embodiment, the geothermal system would generate afixed amount electricity throughout the charge and discharge cycle. Theincrease in thermal energy produced during the discharge cycle isdirected to heat the air stream from the CES process, prior to expansionin a turbine.

There are several advantages when using CES with dispatchablegeothermal:

The heat engine (which converts thermal energy to electricity) is onlysized for the charge cycle, not the peak output of the discharge cycle,dramatically reducing equipment and capital costs.

Minor additional facilities are required to supply heat to the CESfacility.

CES is discharging only over several peak hours in the day. Thedispatchable geothermal system discharging cycle can match the CESdischarging cycle.

FIG. 6 illustrates the thermal output over 30 years of the “Base Case”and “8 Hour Dispatchable Case” referred to in previous Figures. The basecase is operated in baseload manner and equal to the available thermaloutput capacity, while the “8 Hour Dispatchable Case” obtains aneffective capacity factor of ˜97% despite operated in a dispatchableoutput and thus substantially equates with the predetermined potentialthermal output capacity of the formation.

This illustrates the primary invention, that the output can be madedispatchable while still retaining a high geothermal capacity factor,typically over 80% and approaching 100%.

The transient thermodynamic simulations described above were tested in aprototype geothermal system in central Alberta, Canada. The systemincludes a multilateral U-tube heat exchanger 2.4 km deep and 2.5 fromsurface site to site. The results validate the modelling and demonstratedispatchability can be predicted and controlled by modulating the flowrate using, in this embodiment, an automated control valve at the outletwell. The empirical results confirm that the system is very fast rampingand when combined with a power generation system such as an OrganicRankine Cycle (ORC), can meet the fast-ramping requirements ofintegrating with Solar systems.

FIG. 7 demonstrates how the dispatchable geothermal system is used whenintegrated with other non-dispatchable renewables. The system is turneddown during peak hours for Solar and ramped-up as Solar declines. Thedispatchable geothermal fills the gap between the energy demand and thenon-dispatchable renewables. This is only an example and the output canbe modified to match any combination of charging/discharging cycles andthe flow rate can be varied to meet any shaped output within physicallimits.

Solar electricity is used as an example, however, the same dispatchablemechanisms can be used to integrate into direct heat use applicationssuch as district heating systems or in district cooling systems.

FIG. 8 illustrates multiple dispatchable geothermal loops in a network.The charge/discharge cycles may be scheduled for each loop so that theaggregate output meets the required shaped output profile. The flowrate, thermosiphon, and temperatures are controlled in each loop usingan automated control system coupled to a thermodynamic model. The chargedischarge cycles may be sequenced or simultaneous depending on thesituation and the parameters of each loop.

FIG. 9 is a process flow diagram to plan, control, and optimize theintegration of non-dispatchable renewables with dispatchable geothermal.Providing an electrical grid system that has a demand profile over time,existing supply profiles from varying non-dispatchable renewable sourceslike PV, Wind, Baseload Nuclear, etc, the control technology optimizes anetwork of dispatchable renewable geothermal generators to fill the gapbetween the existing non-dispatchable supply profile and the demandprofile. The optimization parameter can be to meet net demand, or it canbe to maximize the price or revenue (price multiplied by volume)received, or any other combination of factors. These may form only apart of the optimization/scheduling algorithm.

In a network of dispatchable geothermal loops, a network of powergeneration modules (not shown) would be utilized which convert potentialand thermal energy into electricity. These power generation systems maybe ORCs, flash plants, pressure drive systems, direct turbines, or anyother conversion means. The power generation modules may be arranged inseries or parallel or a combination. The control system directs flowfrom each geothermal loop to the appropriate conversion module(s) basedon proximity, scheduling, temperature, and other relevant factors.

FIG. 10 illustrates the combined power output capacity of a network ofpower generators which is necessarily higher than the potential thermaloutput capacity of the geothermal loop network. The power generationcapacity is designed to meet the peak output of the geothermal networkwhen dispatching, which may be set to meet the peak demand from theend-user. This figure illustrates that while the subsurface system has ahigh geothermal capacity factor, over 80% and typically over 90%, (wherethe denominator is the potential thermal output capacity), the surfacepower conversion modules have a relatively lower capacity factor toenable dispatching.

FIG. 11 illustrates an embodiment of the invention designed to mitigateelectrical grid saturation with intermittent sources of power. In theexample, a solar recovery arrangement 30 is operatively connected to aloop, L, (loop arrangement or solution) and more specifically to thearray 30 at 32. The power generation device 22 is in electricalcommunication with the grid (not shown) with a specific capacity. Thisis generally denoted by reference numeral 34.

For the following example, loop arrangement or loop solution is intendedto embrace the arrangement discussed herein previously, namely thewells, 14, 16 and interconnection 18 in a thermal bearing geologicformation which may include the power generation device 22.

Solar has a leading place in today's shift to newer cleaner forms ofpower. Success can, however, bring its own complications. Manyelectrical grids are now saturated with wind and solar, to the pointthat it is getting difficult to absorb more intermittent sources ofpower. Scalable green dispatchable power is required in this scenario.The technology herein can complement new or even existing solar plants.

A typical 10 MW loop, L, unit combines a 5 MW subsurface baseloadsolution with an ORC and surface facilities scaled to 10 MW. This is tofacilitate the inherent dispatchability of the energy produced by theloop, L. This may then be further scaled by the simple addition of moreloop arrangements, L. By way of example, a 200 MW loop, L, arrangementhas the following operational data.

Example—Grid Saturation Mitigation

Peak Capacity Average Utilization Load (MW) (MW) Factor (%) LOOPARRANGEMENT Solar Capacity 200 40 20% Loop Capacity 200 100 50%Transmission Capacity 200 140 70% SOLAR ONLY Solar Capacity 700 140 20%Loop Capacity 0 0 N/A Transmission Capacity 700 140 20% SOLAR + BATTERYSolar Capacity 700 140 20% Battery Capacity (8 h) 200 N/A N/ATransmission Capacity 200 140 70%

Solar Only Solution

For a 200 MW solar farm, because of its intermittent nature, wouldproduce on average only 40 MW. In the event that it is desired toincrease the average power production 3.5 times or an additional 100 MWon average, one would have to add an additional 500 MW solar farm and anadditional 500 MW in transmission capacity for the simple reason thatthe solar load factor is going to range between 10% and 25%.Unfortunately, not only does this involve increasing the surfacefootprint 3.5 times, it also requires upgrading the transmission network3.5 times (or more undesirably, building new transmission lines to a newsolar farm). This is further worsened since most of the increasedcapacity would be produced at times of the day where considerably belowaverage prices would be achievable.

The Loop Solution

In contrast, one could achieve the same results by incorporating a 200MW loop solution directly under the existing surface footprint of thecurrent or planned solar farm. Advantageously, no new land acquisitionwould be required. Furthermore, because the loop arrangement would useits inherent dispatchability to produce power around the 20% load factorof the solar farm, there will be no need for any additional transmissioncapacity—saving both time and money. Finally, while the loop would nothave the transmission capacity to produce much during the period of peaksolar production around midday, midday production (which is often oflittle value) could be shifted to attractive monetization because of thepricing premium to be achieved for dispatchable, rather thanintermittent or baseload power.

Solar+Battery Solution

Of course, solar could mimic the loop solution by the addition of enoughbatteries, but at considerable cost. Instead of just adding a 200 MWloop solution, the solar developer would need to add 500 MW of solarcapacity, requiring a massively expanded surface footprint and 200 MW of8-hour battery storage—resulting in inevitable increased costs anddelay.

As a variation to the example, FIG. 11 depicts an arrangement using awindmill 36 as the prime mover.

Referring now to FIG. 12, shown is a further variation to the example.Numeral 40 represents a geographic area on which power distributioncentres 42 are arranged to provide electrical delivery via 44 to thepower transmission grid (not shown). As is known, the grid has an outputcapacity. The centres 42 contribute to a power production system overthe geographic area 40 with a designed maximum power production quantityand a second effective or “real” power production quantity on the grid.

Clearly, over an expanse of area 40 between centres 42, there areoccasionally “brownouts” or other delivery anomalies that occur for avariety of reasons known to those skilled such as is spikes of heavyuser demand or redistribution between centres 42.

In order to alleviate inconsistent delivery issues, loop arrangements,L, may be integrated on the circuit of centres 42, such as betweenadjacent electrically communicating centres 42. As with the previousexamples and specification herein, the closed loop configuration can beprovided within the underlying geologic formation to produce apredetermined energy output from available potential thermal capacityattributed to the formation.

The working fluid can then be circulated as has been discussed andselectively thermally discharged through said power productionarrangement 22 to maintain power production to the capacity throughoutsaid power transmission grid. This accordingly mitigates the anomaliesor irregularities noted above.

Depending on the geographic area and other factors, a main distributionhub 46 comprising a plurality of loop arrangements, L, could augment orreplace some or all of centres 42 and individually positioned loops, L.

1. A method for optimizing the characteristic potential thermal outputcapacity of a well system including a working fluid capable of thermalcharging from said a geologic formation, said system having an inletwell and an outlet well and disposed within a formation, comprising:modulating circulation of said working fluid within said well system tooscillate thermal output from thermally charged working fluid about thecharacteristic predetermined potential thermal output capacity, wherethe averaged oscillated thermal output substantially equates with saidpredetermined potential thermal output capacity of said formation. 2.The method as set forth in claim 1, wherein said thermal output isinconstant.
 3. The method as set forth in claim 1, wherein said thermaloutput is cycled between a charging operation where said working fluidis thermally charged through conductive heat transfer from saidformation and a discharging operation where thermal energy is removedfor processing.
 4. The method as set forth in claim 3, whereinprocessing comprises conversion to at least one of electrical energy,heat energy and combinations thereof.
 5. The method as set forth inclaim 3, wherein modulating includes at least one of variation in flowrate of said working fluid, residency time in said system, oscillationduration, thermal charging duration, thermal discharging andcombinations thereof.
 6. The method as set forth in claim 1, furtherincluding the step of generating on demand energy to an end user throughinteraction between said charged working fluid and a power generationdevice.
 7. The method as set forth in claim 1, wherein said thermallycharged working fluid is circulated above said characteristic potentialthermal output capacity in a discharging cycle to produce on demandpower.
 8. The method as set forth in claim 1, wherein said geologicformation is selected from the group comprising: a geothermal formation,a low permeability formation, a sedimentary formation, a volcanicformation, a high temperature formation, a variable permeabilityformation and combinations thereof.
 9. The method as set forth in claim1, wherein said geologic formation contains no substantial cracks,fissures, voids and or fractures.
 10. The method as set forth in claim1, wherein cracks, fissures, voids and or fractures are induced in saidformation.
 11. The method as set forth in claim 10, further includingthe step of sealing said cracks, fissures, voids and or fractures iscoincident with drilling said wells.
 12. The method as set forth inclaim 10, further including the step of sealing said cracks, fissures,voids and or fractures occurring subsequent to drilling said wells. 13.The method as set forth in claim 1, wherein said working fluid includesa drag reducing additive, a surfactant, a polymeric compound, asuspension, a biological additive, a stabilizing agent, anti-scalingagents, anti-corrosion agents, friction reducers, anti-freezingchemicals, biocides, hydrocarbons, alcohols, refrigerants, phase changematerials, organic fluids and combinations thereof.
 14. The method asset forth in claim 5, wherein said interaction between said chargedworking fluid and said power generator includes minimizing saidresidency time by increasing the flow rate of said charged workingfluid.
 15. The method as set forth in claim 1, further including thestep of storing thermal energy from said charged working fluid in saidformation.
 16. The method as set forth in claim 1, further including thestep of supplementing said working fluid with energy charged workingfluid from adjacent wells in said formation.
 17. The method as set forthin claim 16, wherein supplementing includes rerouting working fluid fromadjacent wells to a well and a power generation device under userdemand.
 18. The method as set forth in claim 1, wherein circulation ofsaid working fluid is effected by an induced thermosiphon.
 19. Themethod as set forth in claim 18, wherein hydraulic pressure loss inoperation is less than 1.5 times the quantity of the thermosiphonpressure.
 20. The method as set forth in claim 18, wherein hydraulicpressure loss in operation is less than 1.0 times the quantity of thethermosiphon pressure.
 21. The method as set forth in claim 1, furtherincluding the step of amalgamating intermittent renewable energygenerating methods with the method of claim
 1. 22. The method as setforth in claim 21, wherein said intermittent renewable energy generatingmethods include wind, solar and electrochemical methods.
 23. A methodfor providing on demand power to an end user with a well system havingan inlet well, an outlet well in a thermally productive geologicformation, comprising: forming a closed loop with a power generationdevice operatively connecting said inlet and said outlet; circulating aworking fluid in said loop with a predetermined residency time tothermally load circulating working fluid through conduction from saidformation; modulating the flow rate of thermally loaded working fluidwithin said loop for power generation based on user demand;interconnecting said inlet well and said outlet well with a plurality ofinterconnecting sections in a predetermined pattern within saidformation; and selectively modulating circulation of said working fluidwithin predetermined sections of said plurality of interconnectingsections of said well system to oscillate thermal output from thermallycharged working fluid about a characteristic predetermined potentialthermal output capacity of said formation, where the averaged oscillatedthermal output substantially equates with said predetermined potentialthermal output capacity of said formation.
 24. The method as set forthin claim 23, further including interconnecting said inlet well and saidoutlet well with an interconnecting section in fluid communication, atleast part of said interconnecting section being disposed for conductionin said thermally productive geologic formation.
 25. (canceled) 26.(canceled)
 27. The method as set forth in claim 23, wherein saidgeologic formation is selected from the group comprising: a geothermalformation, a low permeability formation, a sedimentary formation, avolcanic formation, a high temperature formation, a variablepermeability formation and combinations thereof.
 28. The method as setforth in claim 23, wherein said well system includes pre-existing wells.29. The method as set forth in claim 28, wherein said geologic formationincludes at least one of hot dry impermeable rock, naturally fissured,fractured or cracked rock, synthetically fissured, fractured or crackedrock and combinations thereof.
 30. The method as set forth in claim 24,wherein said interconnecting section is cased, uncased, lined,chemically treated, chemically sealed, thermally sealed, includes singlepipe, coaxial pipe and combinations thereof in a continuous ordiscontinuous configuration.
 31. The method as set forth in claim 23,wherein said inlet well and said outlet well are co-located.
 32. Themethod as set forth in claim 23, wherein said interconnecting sectionsare arranged: symmetrically relative to adjacent interconnectingsections; asymmetrically relative to adjacent interconnecting sections;in interdigital relation to adjacent interconnecting sections; incoplanar relation to adjacent interconnecting sections; in parallelplanar relation to adjacent interconnecting sections; in isolated orgrouped networks; and combinations thereof.
 33. The method as set forthin claim 23, further including the step of providing at least one of aplurality of closed loops with outlet wells of adjacent loopsselectively connected to inlet wells of additional wells, inlet wells ofadjacent wells commonly connected, outlet wells of adjacent wellscommonly connected and combinations thereof.
 34. The method as set forthin claim 33, further including the step selectively modulatingcirculation of said working fluid within predetermined loops of saidplurality of loops of said well system to oscillate thermal output fromthermally charged working fluid about a characteristic predeterminedpotential thermal output capacity, where the averaged oscillated thermaloutput substantially equates with said predetermined potential thermaloutput capacity.
 35. The method as set forth in claim 33, whereinselective connection comprises valved connection with temperaturemonitoring.
 36. The method as set forth in claim 33, wherein theselective connection comprises a daisy chain connection.
 37. The methodas set forth in claim 36, wherein said daisy chain connection is atleast one of continuous, intermittent and combinations thereof.
 38. Themethod as set forth in claim 23, further including the step ofamalgamating said method with intermittent renewable energy generatingmethods.
 39. The method as set forth in claim 38, wherein saidintermittent renewable energy generating methods include wind, solar andelectrochemical methods. 40.-63. (canceled)
 64. A method for providingon demand power to an end user, comprising: providing an inlet well, anoutlet well and an interconnecting section between said inlet well andsaid outlet well and being disposed within a geologic formation having apredetermined potential thermal output capacity, said formation having atemperature of at least 90° C.; connecting said outlet well to a powergeneration device to recover energy from the well arrangement in aclosed loop between the wells and the power generation device; andcirculating a working fluid within said loop at varying flow rates tooscillate thermal output about the predetermined potential thermaloutput capacity, to produce on demand power where the average thermaloutput may equal the predetermined potential thermal output capacity.65. A geothermal power output system having baseload distributionsubstantially equivalent with oscillated discontinuous output cyclesaveraged over a distribution period.
 66. A power plant for providinguser predetermined power distribution, comprising: a thermal energyrecovery apparatus configured to modulate the circulation of a workingfluid in a thermally productive formation whereby thermal energy istransferred into said working fluid, said apparatus for oscillatingdiscontinuous output cycles averaged over a distribution period; anddistribution apparatus for distributing averaged power output as a userpredetermined power output.